DESCRIPTION: This revised application is to support the investigation of the structure and biosynthesis of the polysaccharide components of the LPS molecules involved in Rhyzobial symbiosis. These cell wall polysaccharides are thought to be important determinants of virulence and to be required for the invasion of the host. The overall goal is to determine the structure and biosynthesis of these complex glycolipids and determine the specific structural features required for their biological activity. The specific aims are: 1) characterize the minimum lipidA core structure requirements for the ligation of the O-chain polysaccharide, and characterize the modification to this minimal lipid. A core structure which lead to the ligation of increased O-chain polysaccharide, 2) to characterize the structural modification to the O-chain that occur during the symbiotic infections, 3) to isolate mutants of R. leguminosarum that are unable to add unique structural features normal found in the LPS of this species, and 4) to characterize the R. leguminosarum specific enzymes that process the Kdo2-lipid-IVA precursor to the unique structure of this organism.